Fuels derived from low grade oil, as used in sone diesel engines, have the drawback of containing a high proportion of sulfur compounds. The water generated by combustion facilitates the formation of sulfuric acid under certain conditions of temperature and pressure. This acid corrodes the walls of the cylinder liners, thereby reducing their lifetime.
Experiment has shown that such corrosive wear is low or non-existent for peripheral temperatures of 150.degree. C. However, at 130.degree. C., the combined effects of acid and temperature give rise to maxmium chemical attack.
Providing the engine is working at full load, or close to full load, modern diesel engines have a peripheral temperature which is greater than 150.degree. C. in the most exposed portion of their liners. However, if the engine is used at light load (e.g. 25%), the heat flow through the liner walls is divided by three, and since the flow of cooling fluid through the engine is maintained at constant temperature by a conventional regulator device, there is a correspondingly large drop in the peripheral temperature of the lining and a consequent risk of sulfuric acid attack.
In order to combat this phenomenon, basic lubricating oils are used in order to neutralize the effects of the acid. When the piston is at top dead center, that portion of the liner which is situated below the wiper rings is lubricated by oil which is continually being refreshed; however, that portion of the liner which is situated between the explosion ring and the, or each, wiper ring benefits only from the lubrication oil burnt by the engine, i.e. from about 1/200 of the fuel consumed. This portion of the liner is thus particularly exposed when its temperature reaches a critical value, since the low oil feed rate is insufficient to neutralize the acid.
Preferred implementations of the present invention solve the above drawbacks, while nevertheless reducing regulation parameters and their processing to a minimum.